These applications are, in particular, those in the chemical, pharmaceutical and food fields wherein liquid or gaseous fluids circulating in the systems often must have controlled characteristics of sterility, purity, etc., which in any case should not be altered by passage through the valves.
These applications are, in particular, those in the chemical, pharmaceutical and food fields wherein liquid or gaseous fluids circulating in the systems often must have controlled characteristics of sterility, purity, etc., which in any case should not be altered by passage through the valves.
In practice these valves are usually called “diaphragm” or “membrane” valves, because the member which shuts off the fluid is a flexible closure member made of synthetic material (plastics, rubber, etc.) or metal, which physically separates the path of the fluid circulating through the valve from the control members which are disposed outside thereof, so as to prevent any contamination of the fluid caused by external impurities or by contact with the above-mentioned members, with their lubricants, or with the fluids (compressed air or oil) which are used in the actuators for operating the valves.
It should however be pointed out that the closure members may be of many shapes and sizes, so that their definition as “diaphragms” or “membranes” may therefore sometimes be restrictive or in any case somewhat inappropriate for describing their configuration.
A particular aspect of the invention relates especially to valves for shutting off fluids at high temperatures (120-180° C.), and operating with pressures of the order of 5-10 bar, such as the steam which is used in autoclave sterilization systems and the like.
For these valves, it is important that the movement of the closure member be precise and enable the fluid passage port to be closed completely; however, because of the above-mentioned difficult operating conditions, it is not always possible to achieve these results.
For example, in a valve known from European patent No. 508 658 in the name of Asepco, a fluid passage aperture in the valve body is closed by a flexible silicone-rubber membrane wrapped around a head screwed onto the end of an actuator rod which is moved by a hand wheel. This valve ensures an effective seal by virtue of the resilience of the rubber which forms the membrane, since it deforms and adheres well to the edge of the aperture when compressed against it by the actuator head.
The use of a soft and thin material for building up the membrane in these valves, is also rendered necessary by the fact that the membrane has to be fold in a bellows-like manner around the actuator head on which it is fitted.
However, this means that for building the membrane it is necessary to use materials (such as silicone rubber or the like) which inevitably cannot be very strong, particularly at high working temperatures and pressures, so that the membrane in fact has to be replaced quite frequently in these valves thereby requiring more maintenance and longer stoppage times for the plants in which they are installed.
As an alternative to this type of valve there exhist another one in which the closure member is constituted by a slightly curved, flexible disc having a central core formed integrally therewith; this alternative is described in U.S. Pat. No. 6,123,320 in the name of Rasanow et al.
The core has a shank at its rear end, which is coupled with an actuator and, on its front end, a tip with conical geometry; this tip closes the inlet of a first duct for the outlet of the fluid that is to be shut off, which duct is coaxial with the closure-member disc.
Moreover, a second duct parallel to the first one is disposed in an eccentric position in the seat of the valve body which houses the disc closure member.
In contrast with the previous case, this closure member is made of plastic material such as PTFE, EPDM, or the like, which are not soft like the above-described silicone rubber.
In principle, this type of valve is consequently suitable for withstanding the high temperatures and pressures used in the chemical-pharmaceutical field; however, it has some aspects which significantly limit its performance.
First of all, it should be pointed out that the flow ducts of the fluid passage through the valve body (with reference to the drawings of the above-mentioned American patent), on which the disc closure member acts, in practice renders a valve of this type unusable in an upside-down condition with respect to that shown in this patent.
For example, this is the condition of valves applied to the bottom of tanks, containers, or the like and a solution like that disclosed in Rasanow would lead to inevitable stagnation of fluid in a portion of the ducts and on the closure member, so as to cause the deposition thereon of particles which may prejudice the sterility of the plant and of the chemical processes which take place therein.
Moreover, when the fluid enters the valve through the above-mentioned eccentric duct, it enters the seat of the closure member with a jet directed against the closure disc.
However, the disc is a thin element since it must be able to bend in order to comply with the closure and opening movements of the valve, so that in such circumstances it is inevitably subject to frequent breakage, particularly with fluids at high temperature and pressure like those used for the purposes considered above.
In other words, in this case although the plastic material of the disc closure-member is stronger than the silicone rubber used in the Asepco valve, its conditions of use are such that the advantages potentially obtainable with such a material are lost.
The technical problem underlying the invention is therefore that of improving this prior art; it thus aims at providing a diaphragm valve with structural and functional features, such that the closure member can withstand the high pressures and temperatures of the fluids to be shut off, and that stagnation of fluids inside the valve is eliminated even when the valve is mounted upside down, i.e. with the actuator (manual or driven) positioned below the closure member.
This object is achieved by a valve whose characterising features are stated in the claims appended to this description and that will become clearer from the description of a preferred but not exclusive embodiment of the invention, set out hereinafter with reference to the appended drawings, in which: